The present invention relates to devices for administering liquid medicinal formulations in which the liquid is conveyed through narrow flow channels. In particular, the invention relates to small portable devices such as, for example, dosage dispensers, nebulisers or injectors as used for the measurement, inhalation or injection of liquid medicament formulations. In particular, the invention relates to a nebuliser for nebulising ethanolic and/or aqueous medical formulations having a coarse filter for the depositing of particles which is inserted in a flow channel in front of a discharge nozzle.
From the prior art a multiplicity of medical devices and also specifically nebulisers are known which are operated with a liquid. In most of them the liquid is transferred into storage vessels or containers which contain a plurality of units to be administered by the device, with the result that the flow channels, metering units, delivery openings such as e.g. spray nozzles of the device, are used several times. In the field of nebulisers this applies for example both to propellant-containing metered dose inhalers (MDIs), in which on actuation of a metering valve the propellant gas expels the formulation from a storage container through the same nozzle over and over again, and to purely mechanical nebulisers such as, for example, standard commercial nasal spray systems or finger pump systems.
All these systems are potentially prone to the obstruction of flow channels or discharge nozzles. This obstruction may be caused, for example, by abraded particles during use or during the assembly of the system or by the agglomeration of formulation ingredients.
The occurrence of this obstruction is dependent on the composition of the formulation, the solubilities of its ingredients, the interaction potential of the ingredients with one another and with components of the device in fluid contact and the behaviour of the formulation under different climatic conditions, particularly at different temperatures.
EP 0 521 061 B1 discloses a metering device in the form of a purely mechanical nebuliser in which a measured amount of liquid medicament is conveyed into a pressurised chamber from which the liquid medicament is expelled through a nebuliser head by piston pressure. In the inlet channel of the nebuliser head there is a single filter—in the form of a lattice mesh, for example—for catching particles en route to the discharge nozzle.
A nebuliser with which liquid medicament formulations are nebulised for inhalation from a container holding several units of the formulation has been marketed by Boehringer Ingelheim KG for years under the name “RESPIMAT®”. This purely mechanical miniaturised high pressure nebuliser is shown in WO97/12687A1 and WO09/047173A2. Using this nebuliser a liquid medicament formulation can be nebulised from a rigid container with an inner bag inserted in the nebuliser, as disclosed in WO00/49988A2, conveyed out of the inner bag by means of a piston pump driven by a helical thrust gear and, by means of a spring-operated pressure generator, nebulised in a pre-defined amount through a microstructured nozzle to form an aerosol intended for the lungs. The nebulisation through the nozzle is based on the high speed impact of two microscopic jets of liquid, thus forming a fine mist. Details of possible microstructures for the discharge nozzle inserted in the nebulisers are disclosed in the specifications WO94/07607A1, WO99/16530A1 and WO05/000476A1. WO09/047173A2 describes the flow path of the medicament preparation from the container through a conveying tube into the pressure chamber and from there through a preliminary filter made of plastics into the microstructured discharge nozzle. According to the size exclusion principle, particles of the order of magnitude of the exit channels of the nozzle are trapped in the flow path before the nozzle.
In the specification U.S. Pat. No. 6,837,866B1 there is a description of the use of a filter in a needleless injection system. The active reagent is delivered by a jet of pressurised gas which, like a shock wave, breaks open the membranes between which the active reagent is located. The filter used here, comprising a stack of metallic nets, with a final ceramic layer, does not serve to filter the active reagent itself but purely to filter the pressurised gas and especially to cool it (when the jet of pressurised gas is generated, a pyrotechnic generator is used and the temperatures produced in the process should not come into direct contact with the active reagent).
The starting point for the development shown here is the filtering of liquids which has hitherto been integrated in medical hand-held devices such as the nebuliser described in WO09/047173A2.
The problem on which the present invention is based is to provide a device that is improved compared with the prior art, for administering liquid medical formulations—particularly a hand-held device such as a nebuliser or injector—which contains a filter system designed particularly for small flow cross-sections and designed for the depositing of all kinds of particles. The devices equipped with this filter system should be as independent as possible of their ultimate use, i.e. in particular independent of the choice of solvent in the formulation, the compatibility characteristics and the climatic conditions. The filter system and the associated assembly concept should be suitable for mass production.
In particular, the aim is to provide a filter system in which there is effective filtration of the liquid medical formulation. Particularly preferably, the filter system should filter out even the tiniest residues with a diameter of less than 1 μm from the inhalable solution, or abraded particles. Such tiny particles are not always picked up by typical size exclusion filters, which reliably filter out particles with a diameter at least in the micron range.